Photoresponsive polymers

Abstract

A composition that expands or contracts upon a change in exposure to light energy is provided that comprises a protein or protein-based polymeric material having an inverse temperature transition in the range of liquid water, wherein at least a fraction of the monomers in the polymer contain an light energy-responsive group that undergoes a change in hydrophobicity or polarity upon a change in exposure to light energy and is present in an amount sufficient to provide a shift in the inverse temperature transition of the polymer upon the change in exposure to light energy. Compositions of the invention, including those further containing a side-chain chemical couple, can be used in a variety of different applications to produce mechanical work, cause turbidity changes, cause chemical changes in an enclosed environment, or transduce other free energies by varying the exposure to light energy on the composition. The degree and efficiency of mechanical or chemical change can be controlled by, inter alia, selection of the type, amount, position, and mole fraction of the light energy-responsive side chain group and hydrophobic residues in the polymer.

What is claimed is:  
     
         1 . An photoresponsive bioelastic polymer, comprising: 
 a bioelastomeric polypeptide repeating unit having an inverse temperature transition, wherein at least one amino acid residue in the bioelastomeric unit has a side chain that responds to a change in exposure to light energy to effect a change in polarity or hydrophobicity of the side chain and is present in sufficient amount to provide a shift in the temperature of inverse temperature transition of the polymer upon the change in exposure to light energy.    
     
     
         2 . The photoresponsive bioelastic polymer of  claim 1 , wherein the light energy is in the ultraviolet, visible or infrared range.  
     
     
         3 . The photoresponsive bioelastic polymer of  claim 1 , wherein response of the photoresponsive side chain upon a change in exposure to light energy is isomerization, oxidation, reduction, ionization, deionization, protonation, deprotonation, amidation, deamidation, dimerization, cleavage, or addition.  
     
     
         4 . The photoresponsive bioelastic polymer of  claim 1 , wherein the reaction of the photoresponsive side chain is reversible.  
     
     
         5 . The photoresponsive bioelastic polymer of  claim 1 , wherein only a fraction of bioelastomeric repeating units in the polymer contain said side chain that responds to a change in exposure to light energy.  
     
     
         6 . The photoresponsive bioelastic polymer of  claim 1 , wherein the temperature of inverse temperature transition is in the range of liquid water.  
     
     
         7 . The photoresponsive bioelastic polymer of  claim 1 , wherein the bioelastomeric units are selected from the group consisting of bioelastic pentapeptides, tetrapeptides, and nonapeptides.  
     
     
         8 . The photoresponsive bioelastic polymer of  claim 1 , which further comprises a second amino acid having a side chain capable of undergoing a change in an aqueous environment.  
     
     
         9 . The photoresponsive bioelastic polymer of  claim 8 , wherein said second amino acid side chain undergoes a chemical change.  
     
     
         10 . The photoresponsive bioelastic polymer of  claim 1 , wherein the change in hydrophobicity of the photoresponsive side chain is equal to or greater than the hydrophobicity of a CH2 group.  
     
     
         11 . A composition that expands or contracts upon a change in exposure to light energy, which comprises: 
 a polymeric material having an inverse temperature transition, wherein at least a fraction of the bioelastomeric repeating units in said polymer contain a photoresponsive side chain that responds to a change in exposure to light energy to effect a change in the polarity or hydrophobicity of the side chain and that is present in sufficient amount to provide a shift in the temperature of inverse temperature transition of the polymer upon the change in exposure to light energy.    
     
     
         12 . The composition of  claim 11 , wherein the polymer comprises a series of β-turns separated by dynamic bridging segments suspended between said β-turns.  
     
     
         13 . The composition of  claim 12 , wherein the polymer consists essentially of polypeptide bioelastomeric units, each of which comprises a β-turn.  
     
     
         14 . The composition of  claim 12 , wherein the polymer comprises multiple polypeptide bioelastomeric repeating units, each of which comprises a β-turn, and further comprises intervening polypeptide segments between at least some bioelastomeric repeating units.  
     
     
         15 . The composition of  claim 11 , wherein at least a fraction of said elastomeric units comprise a VPGVG repeating unit.  
     
     
         16 . The composition of  claim 15 , wherein the polymer comprises a segment having the formula poly[ƒ x (VPGXG),ƒ v (VPGVG)] where f x  and f v  are mole fractions with f x +f v =1 and X represents said amino acid residue having a photoresponsive side chain.  
     
     
         17 . The composition of  claim 16 , wherein said polymer comprises a segment having the formula poly[f x (VPGXG),f v (VPGVG),f z (VPGZG)] where f x , f v , and f v  are mole fractions with f x +f v +f z =1, X represents the amino acid residue having a photoresponsive side chain, and Z represents an amino acid residue having a side chain capable of undergoing a chemical change in an aqueous environment.  
     
     
         18 . A method of producing mechanical work, which comprises: 
 changing light energy exposure on a bioelastic polymer containing bioelastomeric units having an inverse temperature transition, wherein at least one amino acid residue in a bioelastomeric unit has a side chain that responds to a change in exposure to light energy to effect a change in the polarity or hydrophobicity of the photoresponsive side chain and that is present in sufficient amount to provide a shift in the temperature of inverse temperature transition of the polymer upon the change in exposure to light energy, and wherein said polymer is constrained so that expansion or contraction of said polymer produces mechanical work.    
     
     
         19 . The method of  claim 18 , wherein when the light exposure is changed an object in contact with the polymer which is under the influence of a force resisted by the polymer moves under the influence of the force as the polymer contracts or expands.  
     
     
         20 . An apparatus for producing mechanical work, which comprises: 
 a bioelastic polymer containing bioelastomeric units having an inverse temperature transition, wherein at least one amino acid residue in a bioelastomeric unit has a side chain that reacts to a change in exposure to light energy to effect a change in the polarity or hydrophobicity of the photoresponsive side chain and is present in sufficient amount to provide a shift in the temperature of inverse temperature transition of the polymer upon the change in exposure to light energy;    means for constraining said polymer wherein expansion of said polymer will produce mechanical work; and    means for applying a change in exposure in light energy to the polymer, whereby a change in the light energy causes the polymer to expand and produce the mechanical work.    
     
     
         21 . A method of producing a pH change in an environment, which comprises: 
 locating in said environment a bioelastic polymer containing bioelastomeric units having an inverse temperature transition, wherein (1) at least one amino acid residue in a bioelastomeric unit has a side chain that reacts to a change in exposure to light energy to effect a change in the polarity or hydrophobicity of the photoresponsive side chain and that is present in sufficient amount to provide a shift in the temperature of inverse temperature transition of the polymer upon the change in exposure to light energy, and (2) at least a fraction of said bioelastomeric units contain at least one amino acid residue with a side chain capable of undergoing reversible protonation, and    applying a change in exposure to light energy to said environment, whereby the light energy change causes a change in the pKa of the polymer and a resulting change of pH in the environment.    
     
     
         22 . An apparatus for producing changes in pH in an environment, which comprises: 
 a bioelastic polymer containing bioelastomeric units having an inverse temperature transition, wherein (1) at least one amino acid residue in a bioelastomeric unit has a side chain that reacts to a change in exposure to light energy to effect a change in the polarity or hydrophobicity of the side chain and that is present in sufficient amount to provide a shift in the temperature of inverse temperature transition of the polymer upon the change in exposure to light energy; and    means for applying a change in exposure to light energy to said polymer, whereby the change in light energy causes said polymer to undergo a change in pKa and change the pH in the environment.    
     
     
         23 . A photoresponsive bioelastic polymer machine of the first order T t -type, comprising the photoresponsive polymer of  claim 1 .  
     
     
         24 . A photoresponsive bioelastic polymer machine of the second order T t -type, comprising the composition of  claim 8 .  
     
     
         25 . A photochemical device for desalinating sea water or brackish water by the conversion of electromagnetic energy to chemical work, which comprises: 
 a) a housing containing an bioelastomeric material capable of stretching in response to a change in exposure to light energy to thereby allow salt-diminished water to move into the bioelastomeric material while substantially repelling solvated salt ions from entry thereto,    b) means for application of a change in exposure of light energy to the bioelastic polymer in the housing,    c) means for uptake of the sea water or brackish water into the housing, means for draining concentrated saltwater from said housing, and means for draining desalinated water from the housing;    wherein the bioelastomeric material is capable of reversibly contracting and relaxing by means of an inverse temperature transition shift induced by light energy.